The present invention pertains to hydantoins substituted in the 5-position by phosphonate containing moieties. These materials are useful as starting materials for preparing flame-retardant polymers particularly epoxy resins, polyesters and polyurethanes.
It has long been known that the incorporation of phosphorus compounds, halogenated compounds, antimony oxide and nitrogen compounds into organic systems imparts varying degrees of flame retardancy thereto depending on the chemical nature of the flame retardant and the organic system being made flame retardant. This subject if reviewed in depth in "The Chemistry and Use of Fire Retardants," J. W. Lyons, Wiley-Interscience, New York, 1970.
Phosphorus is particularly efficacious as a flame retardant in the presence of nitrogen. There often appears to be synergism between these elements with the presence of nitrogen often reducing the need for high amounts of phosphorus, (Lyons, ibid, pp 20-24) to achieve an acceptable level of flame retardancy. Such a combination would exist with the phosphonate hydantoins of the present invention which contain both pendant phosphonate groups and nitrogen molecules in the hydantoin ring.
That such a combination might provide salubrious flame retardant properties in polymeric systems is seen in the teachings of the prior art whereby a variety of reactions hydantoin molecules are substituted in the 3-position by a phosphonate containing moiety as seen in U.S. Pat. Nos. 3,892,765; 3,920,685; and 3,925,406. These prior art hydantoins have only one free --NH-- group available for later glycidylation. The monoglycidyl phosphonate hydantoins described therein are useful as low smoke generating flame retardants for epoxy resin systems, but the heat distortion properties of such resin systems are somewhat lower than unmodified epoxy resin systems due to the monofunctionality of these monoglycidyl phosphonate hydantoins. These hydantoins are monofunctional and therefore lead to less highly cross linked resins than do the phosphonate hydantoins of the present invention. These monoglycidyl phosphonate hydantoins also lead to resin systems with much greater water sensitivity than the resins derived from the phosphonate hydantoins of this invention.
The prior art in U.S. Pat. No. 3,946,034 teaches that hydantoins substituted in the 3-position by a phosphonate containing moiety may form adducts with polyglycidyl compounds which in turn can be used to form epoxy resins having desirable flame retardant properties. The heat distortion temperatures of the epoxy resins formed, however, are still somewhat lower than for unmodified epoxy resins.
In Swiss Pat. No. 456,949 it is taught that dialkyl phosphites can react with polyepoxides to yield reaction products which when cured form moderately flame-retardant epoxy resins. However, the reaction of dialkyl phosphites with epoxides takes place incompletely even with long reaction times.
In U.S. application, Ser. No. 404,835 filed Oct. 9, 1973, now U.S. Patent No. 3,971,813, oligomeric adducts of polyglycidyl hydantoins with dialkyl phosphites are used to prepare flame-retardant epoxy resins having good heat distortion temperature properties. The structure of the adducts involved require some interaction or transesterification between the phosphite molecule and the glycidyl groups and thus have phosphorus atoms in some polymer chains. The instant compounds have pendant phosphonate groups.